1. Field of the Invention
The present invention relates to the control of an elevator. In particular, the invention concerns a method for controlling an elevator that works without changing the torque direction, such as an elevator without counterweight, and a control system designed for applying said method. The control method of the invention is applicable for use e.g. in an elevator without counterweight having an alternating-current electric motor rotating at a relatively high speed and a gear system for adapting the speed for elevator operation.
2. Brief Description of the Prior Art
Elevator control systems nowadays typically comprise an elevator control section and a drive section controlling the electric motor (FIG. 1). The elevator control section comprises traffic control TRC, to which the calls issued from different floors are directed. The drive section again typically comprises motion control MOC, speed control SPC, torque control TOC and a safety circuit SAC. The drive control section receives feedback data giving the position of the elevator car for motion control, the speed for speed control, the motor current for torque control, and safety-related control data from safety contactors, by means of which the supply of current to the motor drive can be switched off to stop at a landing.
In present control systems, between the control blocks a relatively large amount of data traffic, generally serial data traffic is needed for the transmission of signals (generally in serial form). Due to this, present control systems are relatively complex. Moreover, speed control is relatively important especially in the case of elevators having a high capacity (high speed, height). By contrast, in slower elevators having a gear system with a large transmission ratio, speed control is not such a critical factor.